1. Field of the Invention
The present invention relates to an image pickup apparatus having a function of rate conversion processing to deal with the case where a frame rate of recording and a frame rate of reproduction differ from each other, and a control method therefor.
2. Related Background Art
When image data is recorded by an image pickup apparatus capable of switching between NTSC and PAL to reproduce of image data, a frame rate of image data to be recorded differs from a display type of a display apparatus in some cases.
In order to solve this problem, a technique of converting a frame rate is disclosed in Japanese Patent Application Laid-open No. 2004-80327 and Japanese Patent Application Laid-open No. 2004-48530.
For example, Japanese Patent Application Laid-open No. 2004-80327 discloses a method of performing frame rate conversion processing using thinning-out to output image data in conformity with a display rate when a frame rate of image data to be recorded differs from that during reproduction. In this method, for example, if image data recorded in the NTSC (60 fps) standard is to be displayed in the PAL (50 fps) standard, one image is thinned out from every six images to achieve frame rate conversion as shown in FIG. 3.
According to such a conventional method, however, sudden frame dropping occurs. Therefore, there is a problem that the reproduction of a moving image seems to be unnatural.
Moreover, Japanese Patent Application Laid-open No. 2004-48530 discloses a method of weighting two adjacent frames on the basis of an image and assigning evaluation values to all the frames to suppress the unnaturalness caused by the frame dropping. Base on the evaluation values, a frame to be thinned out is selected.
In order to carry out such a conventional method, however, it is necessary to temporarily store a plurality of frames to determine a frame to be thinned out. Accordingly, a large-capacity memory is required. Furthermore, since arithmetic processing for selecting the frame to be thinned out is required, this method is disadvantageous in that delay time from the readout of image data to image display is prolonged. If the delay time is prolonged in this manner, the method is not suitable for displaying images on a view finder during photographing.